Steam generator of the water tube type



Dec. 3, 1935. L RR 2,022,728

STEAM GENERATOR OF THE WATER TUBE TYPE Filed. D30. 23, 1930 T F. 75c 27 x 75 75a 75 75a 756 756 V M" Z HA I NVENT El l=\. mam {MN 5V I 7 L aw Dam;

Patented Dec. 3, 1935 UNITED STATES PATENT OFFICE STEAM GENERATOR OF THE WATER TUBE TYPE

Application December 23, 1930, Serial No. 564,261 In Switzerland December 30, 1929.

3 Claims.

This invention relates to steam generators of the water tube type in which the working mediumwhich need not necessarily be water-is converted into steam or other vapour in a system of tubes, the amount of fuel and water or other working medium supplied being regulated in accordance with the temperature at which the vapour escapes from the outlet end of the tube system.

Such methods of control have not proved satisfactory as the temperature of the steam or the like at the outlet end of the tube system does not quickly respond to changes which take place in the tubes themselves, 1. e. there is a considerable lag due to the heat stored in the wall of the tube system itself and as a result of this lag it is impossible to avoid marked fluctuations in the condition of the steam delivered by the generator.

To meet this difficulty proposals have already been made to vary the supply of feed water in accordance with the temperature of the liquid in the generator prior to its conversion into steam, but this method of regulation prevents compensation for temperature fluctuations due to irregular firing; or variations in the temperature, and the rate of evaporation in that part of the tube system where the liquid is converted into steam, so that the steam discharged is still subject to temperature fluctuations.

The object of the present invention is to prevent the lag to which the temperature of the outlet steam is at present subject owing to the heat stored in the wall of the tubes.

According to this invention the supply of the working medium and fuel is regulated in accordance with the temperature of the working medium at or about that point-in the length of the tube system where the working medium is converted from the saturated into superheated steam or vapour.

The invention is diagrammatically illustrated by way of example in the accompanying drawing, in which Figure 1 shows a steam generator in which the supply of the working medium and fuel is. regulated in accordance with the temperature of the working medium in the tube system, and

Figure 2 is a diagram showing the temperature curve in the tube system under different working conditions.

The working medium, for example water, is supplied to the system of tubes 2 within the combustion chamber not shown through a pipe 3 and the steam generated in the tubes is conveyed to the points of consumption through the main steam delivery pipe 4.

Fuel is supplied to the burner 5 through a pipe 6, the air to support combustion being delivered through a pipe 1. The supply of water or other 5 working medium is regulated by a valve 9 and a valve is? is provided to regulate the supply of fuel, the steam delivered to the main supply pipe 6 being regulated in any desired manner.

The working of the generator will be best seen 10 from the diagram illustrated in Figure 2, in which the length l of the system of tubes is plotted horizontally between the inlet end E and the outlet end A, the temperatures of the working medium at the various points in the system of tubes being plotted vertically.

The curve l2 shown in full lines represents the normal state in the system of tubes. First the working medium which is still in the liquid state is heated to the temperature of evaporation V between the inlet point E and the point. I3. Thereafter to the point it it is converted into saturated steam containing no unevaporated liquid. At this stage there will be a small drop in the temperature of the steam in accordance with the fall of pressure, and subsequently this saturated steam is superheated to the temperature U between the point 14 and the point of discharge l5 from the system of tubes.

In undergoing the change of state between the inlet and outlet ends of the tube system as shown in Fig. 2 a quantity of heat is distributed approximately as to three-tenths for the heating of the liquid medium six-tenths for evaporation and one-tenth for superheating.

When it is desired to increase the output of the boiler i. e. when. the quantity of feed liquid is increased, the temperature of the working medium in the system of tubes 2 will change in the manner indicated by the curve I201. The beginning of evaporation of the working medium is shifted from the original point l3 to a later point I311. As before, the original point [4 at which the working medium was evaporated is now shifted to point lia. The quantity of heat required for superheating the working medium is so small relatively to the quantity of heat required to efiect evaporation, that the heat stored in the wall of the tube system is enough for superheating to the temperature U until the discharge point [5a is reached.

Consequently, although for the increased output more feed water or other working medium has been supplied, the change in temperature at the point of discharge will be only very small 55 owing to the heat stored in the tubes and. the small amount of heat required for superheating. Within the tube system, however, considerable fluctuations in temperature will occur and these will continue until the increased quantity of working medium has been continuously supplied for a considerable period, by which time the heat stored in the tubes will be used up between the points i i and i5 with the result that there will be a sudden drop in the temperature of the steam delivered at the outlet end from that of superheated to saturated steam.

The new curve of temperatures of working medium within the tube system will in this case be that represented by the curve i2b. The point l3 where evaporation begins and the point I4 where it is completed are shifted still further towards the outlet end of the system to the points [3b and Mb. The liquid working medium and the mixture of liquid and steam between the points 83b and Mb absorb from the Wall of the tubes so much of the heat stored in this wall that there is insufficient heat left in the tubes to superheat the steam after the point i ib has been reached. The sudden change in the temperature of the steam at the outlet from the points i5a to 55b cannot be avoided so that either saturated steam or steam containing liquid particles will be delivered instead of superheated steam.

This sudden fall of temperature has many drawbacks. For example, engines driven by this steam are liable to be damaged owing to the priming caused by the rapid fall of temperature. Further, the material from which the generator itself is formed will be adversely aifected by these rapid falls in temperature either through changes in the inner structure of the material itself or through temperature stresses produced.

When the output of the generator is reduced,

less feed liquid is supplied toit. The smaller quantity so supplied will be heated more quickly in accordance with the curve illustrated at I20,

pleted to the point I40. The small amount of heat transmitted to and absorbed by the steam from the tubes between the points He and IE0 is unable to effect any appreciable change in the temperature of the tube wall, so that the temperature of the steam at the point of discharge will only be raised to a negligible extent, that is from the point it; to the new point I50.

Only after a considerable time will a change in temperature at the outlet end of the tube system be perceptible, as in the case when the load is increased, but then this change will take place rapidly and the temperature will quickly rise to a dangerous extent. Such fluctuations lead to irregular working of the engine or apparatus driven by the engine.

According to the invention both the working medium and the fuel is regulated in accordance with the temperature of the working medium at a point in front of the outlet end of the tubes, in Figure 2 this point is indicated at I6. As will be seen from the diagram, the point at which the temperature-responsive device is placed is prefer ably behind the point at which the steam is com pletely evaporated in the tubes, at which point large changes of temperature take place in the tube system directly upon any alteration occurring in the load, thus enabling a quick and eiTective regulation of the generator to be obtained. Such a method avoids the drawbacks of existing steam generators in which evaporation takes place in a system of tubes and regulation is efiected in accordance with the temperature of the steam delivered, for in such existing arrangements, owing to lag, the whole process of regulation is exposed to such fluctuations that effective working is almost impossible. As compared with such existing methods the regulation in accordance with the present invention enables fluctuations in the temperature of the steam generated to be practically eliminated and the improved regulating means can be readily set or adjusted.

In the steam generator illustrated in Figure 1,

changes in the length of the'tube system due to al-,

terations in the temperature are employed to effeet the control of the admission of the working medium and the fuel. At the points 25 and 26, before the. outlet is reached; the system of tubes is arranged in the manner diagrammatically shown in Figure 1, so as to extend outside the combustion chamber. Changes in the length of exposed tube 31 between the points 25, 26 caused by changes in the temperature of working medium flowing through this tube, are used to control both the fuel supply and feed water valves I0 and 9.

The length of pipe 3| is connected at the point 25 to a fixed support and the lever 29 is coupled by a link. 21 to this fixed point. Connected to the lever 29 is a link 30, the lower end of which is connected by a pivot 28 to an arm 26 on the pipe 3i. .When the temperature of the working medium in the pipe 3| rises, the link will be moved downwards and the lever 29 therefore brought into the position 2911 shown in chain lines. The rod 32 connected to the setting lever of the valve 9 will therefore be moved downwards into the position shown at 32a, and the valve 9 will be opened for the supply" of additional working medium.

The lever 34, which can freely turn about the pivot 33, will simultaneously be moved into the position 34a shown in chain lines, and the rod 35 into the raised position shown by chain lines at 35a, so that the valve for the supply of fuel will be closed. The pipe 3i is connected to the main system of tubes 2 at or about that point where, under normal conditions, the working medium first begins to change from saturated to superheated steam.

By this increased supply of feed water or other working medium through the pipe3, and the reduced supply of fuel through the pipe 6, the temperature of the working medium flowing through the tube system 2 will be reduced until normal working temperature is resumed between the points 25 and 26 in the length of tube, when the valves}! and I0 will be moved back to their original position. Should the temperature of the working medium in the length of pipe 3| fall, the valves 9 and III will be moved in the opposite manner so that the supply of. working medium will be reduced and the supply of fuel will be increased, the temperature in the tube system being thus restored to its normal value.

It will be understood that instead of depending on the temperature at the point l6 (Figure 2) where evaporation of the working medium has already been completed, an additional heat-responsive element may be introduced say at the point lea. (Figure 2) where the working medium is still liquid, it being essential that this additional temperature-responsive point should be in advance of the outlet where the temperature retardation has only a minor effect on the degree of regulation.

It will also be understood that the invention can be carried into practice without necessarily adopting any of the particular constructions above described, and that instead of the thermoelements or thermostatic devices specified, any other known suitable device may be employed. The number of revolutions of the pumps may be used to regulate the quantity delivered, or the stroke or clearance, or by-pass or throttle valves may be used for this purpose.

The steam generator may be supplied with solid, pulverized, gaseous or liquid fuel, the regulation of which can be effected in any convenient manner, and any working medium which lends itself to evaporation may be used without departing from the invention.

I claim:

1. A steam generator, comprising at least one tube for the working medium, means for heating said tube, means for supplying working medium to said tube, means for supplying fuel to the heat-producer, and a single means for regulating both the quantity of the working medium and the fuel delivered to the generator by the changes in temperature, only, of the working medium, said means being located at that point in the tube where, under normal conditions, the workgins to change from saturated to superheated steam, by automatically regulatingboth the operating supplied to said generator to maintain the temperature of the output steam constant.

3. A steam generator comprising at least one tube for the working medium, means for heating said tube, means for supplying working medium to said tube, means for supplying fuel to the heat-producer, and a single heat-responsive device formed as a loop of appreciable length of the Working medium conduit and located at that point in the tube system where the working medium under normal conditions first begins to change from saturated tosuperheated steam, for singly controlling the entire generator by automatically regulating the operating supplies to the generator.

- ARTHUR LIEBERHERR. 

